If you click on About Evernote and press the Option key, you'll get a link to your database folder

You can get the size of the database on your Mac This should be
complete, unless you have local notebooks on other computers. I have
two accounts 1.86GB and 5.76GB The database for each account is under
a number folder for example 123456

Space used on the servers would be similar, but not include local
notebooks So it could be less space; however for me, the important
number is the space taken up on my computer